Among piperidin-4-one derivatives useful as an intermediate for agricultural chemicals or pharmaceutical products, it is known that an isotropane derivative having cross-linked structure is produced, for example, by a method wherein cyclopentanone is cyclized in One Step by using a Double Mannich reaction, as shown by the following formula (Patent Reference 1).

On the other hand, as an improved method of the Double Mannich reaction, a method is known wherein a chain bis(aminol)ether is reacted with a cyclic ketone in the presence of a Lewis acid (see Non-patent Reference 1).
    Patent Reference 1: Published Japanese translation of PCT International Publication No. 6-506443    Non-patent Reference 1: Synlett, 2004, (13), 2359-2363